Selective bird feeders are well known in the art and are designed to limit the maximum size of a bird or animal which can access the seeds in the feeder. There are many reasons for excluding certain birds and animals including the fact that certain birds may be regarded as undesirable. Thus, many people only wish to have the smaller birds present at the feeder and not the larger birds. Some of the larger birds such as crows, grackles, blue jays and the like are considered by some people to be undesirable.
A further problem associated with bird feeders is those animals which gain access to the seeds and which can devour a large quantity of seeds in a relatively short period of time. Squirrels in particular are well known for their ability to reach the seeds in bird feeders and have shown great ingenuity in overcoming many devices such as baffles which have been utilized in an attempt to solve the problem.
One of the more popular types of bird feeders which are often referred to as squirrel proof are those which use a movable shroud. Thus, one may refer to U.S. Pat. No. 4,646,686 to Furlani which teaches a movable shroud. A slightly different arrangement is shown in U.S. Pat. No. 3,145,690 to Bachman wherein there is an arrangement wherein an inverted cylinder hopper is suspended over a feeding pan while a bird perch surrounds the pan and is attached to a conical shroud. Heavier birds or animals on the perch cause the shroud to move downwardly.
Other arrangements are shown in U.S. Pat. Nos. 3,126,870; 6,543,384; 6,253,707 and 6,591,781. All of the teachings thereof are incorporated herein by reference.